Plasma processing is widely used in the semiconductor industry for deposition, etching, resist removal, and related processing of semiconductor wafers and other substrates. Plasma processing equipment can be used, for instance, in photoresist stripping applications in integrated circuit fabrication. Photoresist applications following ion implantation for advanced nodes (e.g., nodes of 20 mm or less) can pose challenges. For instance, a hardened “crust” can be formed on a photoresist which has received most of the ion dose during implantation. The remaining photoresist which has not been implanted (e.g., the “bulk” photoresist) can be partially or completely enveloped by the crust.
It can be desirable to cleanly remove the photoresist after ion implantation before the substrate goes to thermal annealing for dopant activation so that there is no residue as residue can lead to a drop in yield. In some instances, this can be accomplished by: (1) plasma strip followed by wet clean; (2) plasma strip only; or (3) wet strip only.
Resist ash strip processes in a plasma stripper can be isotropic processes. A resist ash strip process can remove the crust at the bottom of the photoresist, and can then remove the bulk photoresist. If photoresist is completely removed using a plasma strip process, some residue may not be cleaned by a following wet strip due to the residue hardening during the plasma strip. As a result, for advanced nodes (e.g., 20/16 nm nodes), many manufacturers have switched to wet strip only for use in post ion implantation resist strip. Use of wet strip only can reduce oxidation. However, if the photoresist is removed by wet strip only, a more aggressive chemistry may be needed to remove a crust layer formed during ion implantation. This can attack the substrate and induce defects.